1. Field of the Invention
The present invention relates to an ink jet printer, and, more particularly, to an ink jet printer having a paper handling assembly and a maintenance station assembly for contacting the printhead.
2. Description of the Related Art
Ink jet printing systems can generally be divided into two types: one type using thermal energy to produce a vapor bubble in an ink filled channel that expels a drop of ink; or another type using a piezoelectric transducer to produce a pressure pulse that expels a droplet from a nozzle.
Thermal ink jet printing systems use thermal energy selectively produced by resistors located in capillary-filled ink channels near channel terminating nozzles or orifices to vaporize momentarily the ink and form bubbles on demand. Each temporary bubble expels an ink droplet and propels it towards a recording medium. The printing system may be incorporated in either a carriage-type printer or a pagewidth type printer. The carriage-type printer generally has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is reciprocated to print one swath of information at a time on a stationarily held recording medium, such as paper. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath, so that the next printed swath will be contiguous therewith. The procedure is repeated until the entire page is printed. For an example of a carriage-type printer, refer to U.S. Pat. No. 4,571,599 to Rezanka. In contrast, the pagewidth printer has a stationary printhead having a length equal to or greater than the width of the paper. The paper is continually moved past the pagewidth printhead in a direction normal to the printhead length and at a constant speed during the printing process. Refer to U.S. Pat. No. 4,463,359 to Ayata et al for an example of a pagewidth printhead. Refer to U.S. Pat. No. 4,829,324 to Drake et al (the disclosure of which is herein incorporated by reference) for another example of a pagewidth printhead.
Piezoelectric activated ink jet printing systems use a pulse generator which provides an electric signal. The signal is applied across crystal plates, one of which contracts and the other of which expands, thereby causing the plate assembly to deflect toward a pressure chamber. This causes a decrease in volume which imparts sufficient kinetic energy to the ink in the printhead nozzle so that one ink droplet is ejected onto a recording medium. Refer to U.S. Pat. No. 4,144,537 to Kimura et al for an example of a piezoelectric activated ink jet printer.
In the ink jet printing systems of the above-types, several problems have arisen which adversely affect the quality and performance of printing. Among these problems are 1) clogging of the printhead nozzle caused by ink drying therein due to non-use for a period of time; 2) adherence of dust to the face of the nozzle due to the moisture of fluid ink around the nozzle; 3) leakage of ink from the nozzle; 4) bubbles and dust taken into the printhead nozzle as a result of external causes such as vibration imparted to the printhead and environmental change occurring around the printhead; and 5) contamination of the printhead nozzles when the printhead is not in use such contaminating being, for example, non-collapsing air bubbles.
Several approaches have been proposed which address the aforementioned problems.
U.S. Pat. No. 4,437,105 to Mrazek et al discloses a cassette comprising a capping and cleaning device for the cleaning of an ink jet printhead. The device is operated by moving the printhead into a position in front of a capping window or cleaning window, depending on which function is required. The cassette is then displaced until contact is made between the printhead and the cleaning member or capping member. The cassette may also house a purging position which can collect ink from the printhead during a purging operation and a scraper for scraping off ink from the printhead surface.
U.S. Pat. No. 4,144,537 to Kimura et al discloses a method and apparatus for capping a nozzle of an ink jet recording device. The capping member is located at a position away from (along side of) the printing area. When printing is not being performed, the printhead is moved to this position and is capped. A spring and cam mechanism is used to position the capping member in engagement with the printhead nozzle.
U.S. Pat. No. 4,853,717 to Harmon et al discloses a service station for an ink jet printer comprising a pump for priming a printhead, a sled to actuate the service station and seal the printhead, and a wiping member for cleaning the printhead. The service station cleans clogged nozzles, covers the nozzles with a protective cap when not in use and wipes contaminants from the nozzles. The service station is used with a carriage-type printhead and is fixed at one end of travel of the printhead.
U.S. Pat. No. 4,369,456 to Cruz-Uribe et al discloses a cleaning device for writing heads of an ink jet printer. The apparatus comprises rotatable supply and takeup reels, a movable absorbent cleaning belt including a plurality of embossed elements and a plurality of openings for allowing printing on a paper medium. The cleaning apparatus performs its functions while the printhead remains stationary.
The above-discussed devices attempt to overcome the shortcomings associated with the use of ink jet nozzles With the exception of U.S. Pat. No. 4,369,456, however, all of the devices require movement of the printhead from its operative position for maintenance to be performed thereon. This movement is undesirable as it requires additional moving parts. Such systems are particularly undesirable for use with a full width (pagewidth) printhead. This type of printhead should be held fixed because it is quite large and cumbersome. Additionally, since most of the above-mentioned patents locate the maintenance system adjacent the paper conveying system (e.g., a platen) and require the printhead (which is a carriage-type printhead) to be moved along-side of the paper conveying system, they cannot be practically used with a full width printhead since the printer would have to be made exceptionally wide. Further, since it is required to locate the printhead close to the paper medium for improvement of print quality, it is difficult to locate a maintenance system between the printhead and the paper conveying system. Since both the pagewidth printhead and paper conveying system are large, it is not desirable to move them apart from one another to allow a maintenance system to access the printhead. In the thermal ink jet printhead, and, in particular, the four-color thermal ink jet printhead, heat management often requires a large costly heat transfer unit (heatsink) to dissipate the heat out of the printhead. The use of a fixed printhead would serve to simplify the electrical connections thereto, the ink pathway provided therein and the heat management system connected thereto. These simplifications would lower costs and improve reliability of the printer.
While U.S. Pat. No. 4,369,456 utilizes a stationary printhead, the system does not enable a plurality of maintenance station functions to be performed at a single stationary position of the printhead. Furthermore, the cleaning belt is positioned between the printhead and paper handling system which could result in interference with a printing operation and require additional spacing between the printhead and paper handling system.